PARIS—France has detained 11 armed neo-Nazis around the country, the interior ministry said Friday, amid fears of an anti-Muslim backlash following the terror attacks committed by Islamist radicals in Brussels last week.

The police also found 11 rifles, two handguns, knives, bulletproof vests and Nazi paraphernalia during the operations, which took place Wednesday, the ministry said, adding that the men were distributing xenophobic messages.